Fuel cell electric vehicles broadly employ four major power components: a fuel cell system (FCS), an energy storage system (ESS) such as battery pack, a DC/DC converter (DC/DC) and an electric traction motor. During ordinary driving conditions, in order to achieve high fuel economy, the power distribution between the FCS and ESS is scheduled in a manner such that power consumed by the electric traction motor is fully provided by the FCS whenever possible, and the ESS power delivered through the DC/DC converter is scheduled only when the power response of the FCS (which is relatively slow compared to that of the ESS) cannot meet the power demanded by the motor during transient conditions, such as a fast acceleration or regeneration braking. The scheduling of the power distribution between the FCS and ESS described above is sometimes referred to as a load following power control strategy.
During vehicle acceleration, any overshoot of the motor current and power consumption (which is nearly inevitable during ordinary driving conditions) can lead to over-current or over-power of the FCS if the ESS is not able to absorb this overshoot in sufficient time. The fuel cell over-current may damage the FCS, thereby leading to shutdown of the vehicle, or reduce FCS service life.
In order to protect the FCS against damage resulting from over-current/over-power as described above, a control strategy is followed in which a current/power buffer or reserve is set aside when onboard control systems schedule the current/power available for motor use. In other words, less than the maximum FCS current/power capacity is scheduled for actual motor use. Although this buffering technique is helpful in protecting the FCS against the affects of over-current/power, it results in under utilization of the FCS, which is one of the most important components in the fuel cell electric vehicle power system.
Accordingly, there is a need in the art for a control method that regulates current/power in the fuel cell during transient load conditions, which allows maximum FCS current/power to be scheduled for motor use while protecting the FCS against over-current/power. The present invention is intended to satisfy this need.